1. Field of the Invention
This invention relates to an organic electroluminescent (EL) element, more specifically to an organic EL element with an improved sealing structure.
2. Prior Art
An organic EL element is a current-driving type luminescent element and a large current must be flown between an anode and a cathode. As the result, the element becomes hot when light is emitted. When oxygen or moisture exists around the element during electroluminescence, oxidation is promoted to deteriorate the element. Main defect caused by deterioration due to oxygen and moisture is to generate a non-luminescent point so-called dark spot which is caused by change of properties of the organic material or peel off of the cathode. The dark spot grows up little by little accompanying with deterioration and becomes not to emit light. To prevent the above-mentioned deterioration, various proposals have been made.
In Japanese Laid-Open Patent Application No. 41281/1997, as a method for removing water component, an EL element is holded in an inactive liquid of a fluorocarbon oil containing a dehydrating agent such as a synthetic zeolite, etc.
In Japanese Laid-Open Patent Application No. 114486/1997, a fluorocarbon oil 12a as a heat emission layer is sealed with a sealing glass 9 on at least one of a cathode 2 and an anode 7 as shown in FIG. 5 so as to emit Jourl heat during its operation.
Further, as shown in FIG. 6, it has been known a method of preventing permeation of oxygen or water by providing a seal protective layer 8 of a carbonate compound.
According to the foregoing prior art, however, dark spots generate and grow in many cases due to dissolved oxygen or dissolved water contained in the fluorocarbon oil itself. Also, since a large amount of a dehydrating agent must be added to a sealing member, the element is tended to be damaged thereby, and water taken in the dehydrating agent proceeds oxidation of the element due to direct contact therewith. Thus, it is difficult to suppress formation and growth of dark spots. Also, when sealing is performed by a resin or a metal layer alone, it is difficult to completely prevent permeation of oxygen or water from outside so that an element having a long lifetime of several thousands to several ten thousands hours needed for a final product can hardly be obtained.